Current data center environments implement bulk storage as a block level service for use by software. The actual access behavior of the block accesses have many different variables that include the number of processes running on the computer, the priority of these messages, and the nature of interaction of user Input/Output (I/O) with the software.
Prefetching is a technique used for improving the performance of disk and memory systems. Nominal prefetching increases performance by keeping copies of accessed data, in the hope that the cached data will be accessed again. The information required for a successful prefetch algorithm includes:
What data to prefetch
The circumstances under which the prefetch occurs
The length of time to keep prefetched data cached (if no access occurs)
If the wrong data is prefetched, no accesses to the data will occur and no performance improvements will be realized. Likewise, if the right data is fetched at the wrong time, it may be replaced (by other caching data) before the access occurs. Incorrectly specifying the “keep time” will have a similar effect.